Polymers find uses in a variety of plastic articles including films, sheets, fibers, foams, molded articles, adhesives and many other specialty products. The majority of this plastic material ends up in the solid waste stream, headed for rapidly vanishing and increasingly expensive landfill space. While some efforts at recycling have been made, the nature of polymers and the way they are produced and converted to products limits the number of possible recycling applications. Repeated processing of even pure polymers results in degradation of material and consequently poor mechanical properties. Different grades of chemically similar plastic (e.g., polyethylenes of different molecular weights, as used in milk jugs and grocery sacks) mixed upon collection can cause processing problems that make the reclaimed material inferior or unusable.
Absorbent article applications such as diapers, sanitary napkins, pantiliners and the like, involve several different types of plastic. In these cases, recycling is particularly costly because of the difficulty in separating the different components. Disposable products of this type generally comprise some sort of fluid-pervious topsheet material, an absorbent core, and a fluid-imperious backsheet material. Such absorbent structures are typically prepared using, for example, topsheet materials prepared from woven, nonwoven, or porous formed-film polyethylene or polypropylene materials. Backsheet materials typically comprise flexible polyethylene sheets. Absorbent core materials typically comprise wood pulp fibers or wood pulp fibers in combination with absorbent gelling materials.
A conventional disposable absorbent product is already to a large extent compostable. A typical disposable diaper, for example, consists of about 80% of compostable materials, e.g., wood pulp fibers, and the like. In the composting process soiled disposable absorbent articles are shredded and commingled with organic waste prior to the composting per se. After composting is complete, the non-compostable particles are screened out. In this manner even today's absorbent articles can successfully be processed in commercial composting plants.
Nevertheless, there is a need for reducing the amount of non-compostable materials in disposable absorbent articles. There is a particular need to replace polyethylene and polypropylene topsheets in absorbent articles with liquid pervious compostable material.
In addition to being compostable, materials used for topsheets must satisfy many other performance requirements for satisfying the end user's needs. For example, these materials must be capable of being processed to provide substrates that are comfortable to touch. In addition, topsheets must possess sufficient properties such as impact strength, moisture transmission, etc.
Certain biodegradable resins are well known, but often do not have good fiber or film forming properties. Polymer resins comprising poly(hydroxybutyrate) (PHB) are particularly ill-suited for fiber and film formation. These resins are typically of slow crystallization rates, have low melt viscosity, degrade near their melt temperatures and are rigid when solidified. Accordingly, such resins often cannot be processed by conventional means of film or filament formation. Indeed, when formed into films, biodegradable resins comprising PHB are generally not flexible. The inflexibility of such films hinders their use in absorbent articles, particularly when used as topsheets, as these materials are in direct contact with the skin of the wearer.
For the foregoing reasons, there is a continuing need for biodegradable materials that can be used in absorbent articles. In particular, there is a need for a biodegradable substrate which is flexible and durable, but also provides a comfortable texture when used in, for example, absorbent articles.
It is an object of the present invention to provide biodegradable fibrils that can be processed to give flexible, nonwoven fabrics which are soft and clothlike to the touch. A further object of the invention is to provide a process for making such biodegradable fibrils. Another object is to provide a biodegradable nonwoven fabric comprising biodegradable fibrils. Still another object is to provide disposable absorbent articles comprising such biodegradable fabrics. Still another object is to provide textiles comprising biodegradable fibrils.